1. Field of the Invention
The present invention relates to a giant magnetoresistance element (hereinafter, referred to as a GMR element) and a current sensor using the GMR element.
2. Description of the Related Art
Recently, a magnetic sensor which detects a magnetic field has been widely used in magnetism application products which have been widely used. In addition, as an application of the magnetic sensor, a current sensor which measures a current without contacts by detecting a magnetic field generated by current that flows through a conductor has also been widely used. Furthermore, the current sensor is used for measuring a relatively low current without contact as in electric appliances at home, or is used for measuring a relatively high current without contact as in an electric vehicle, a hybrid car, or the like.
FIG. 8 is an explanatory view of a current sensor disclosed in Japanese Unexamined Patent Application Publication No. 2007-121283. As illustrated in FIG. 8, a current sensor 110 disclosed in Japanese Unexamined Patent Application Publication No. 2007-121283 is configured so that magnetoresistance elements 101 such as GMR elements which are formed in a semiconductor chip 116 are embedded in a housing 117. In addition, the current sensor 110 is disposed at a predetermined position on a conductor 111 though which current flows, and measures the current by detecting a magnetic field generated by the current.
FIG. 9 is an explanatory view of a GMR element disclosed in Japanese Unexamined Patent Application Publication No. 2004-164837. As illustrated in FIG. 9, a GMR element 201 disclosed in Japanese Unexamined Patent Application Publication No. 2004-164837 has a structure in which an antiferromagnetic layer (PtMn) 205, a fixed magnetic layer (CoFe/Ru/CoFe) 206, a spacer layer (CuO) 207, a free magnetic layer (CoFe/NiFe) 208, and a protective layer (Ta) 209 are laminated in this order.
As described above, in Japanese Unexamined Patent Application Publication No. 2004-164837, the free magnetic layer 208 has a structure in which CoFe having a high spin polarizability and NiFe having excellent soft magnetic properties are laminated. Therefore, the GMR element having a high resistance change ratio ΔR/Rmin and a small degree of hysteresis in a magnetization curve can be realized.
In addition, as the magnetism application products, there are a magnetic head of a hard disk drive, and a tunnel magnetoresistance element (hereinafter, referred to as a TMR element) which is generally used as a magnetoresistive random-access memory (MRAM).
FIG. 10 is an explanatory view of a TMR element disclosed in Japanese Unexamined Patent Application Publication No. 2010-097981. As illustrated in FIG. 10, a TMR element 301 disclosed in Japanese Unexamined Patent Application Publication No. 2010-097981 has a structure in which an antiferromagnetic layer (IrMn) 305, a first fixed magnetic layer (CoFe) 306a, a non-magnetic intermediate layer (antiferromagnetic coupling layer) (Ru) 306b, a second fixed magnetic layer (CoFeB) 306c, a tunnel barrier layer (MgO) 307, a free magnetic layer 308, and a protective layer 309 are laminated in this order.
It is known that the TMR element 301 can obtain a high resistance change ratio ΔR/Rmin (MR ratio) by allowing MgO of the tunnel barrier layer 307 to be crystallographically oriented in the (001) direction. In addition, it is known that MgO is crystallographically oriented in the (001) direction of a rock-salt structure by being formed on an amorphous base layer. Therefore, in Japanese Unexamined Patent Application Publication No. 2010-097981, the tunnel barrier layer (MgO) 307 is formed on the second fixed magnetic layer (CoFeB) 306c which is formed as an amorphous film.
In Japanese Unexamined Patent Application Publication No. 2010-097981, thereafter, CoFeB of the second fixed magnetic layer 306c which is formed as an amorphous film is allowed to follow the crystal structure of the MgO interface of the tunnel barrier layer 307 and is crystallized by a heat treatment. The reason for this is that CoFeB of the second fixed magnetic layer 306c has a body-centered cubic structure on the surface side which comes into contact with the tunnel barrier layer (MgO) 307 and is crystallographically oriented in the (001) direction, and thus a high resistance change ratio ΔR/Rmin is realized. However, this structure is a structure unique to the TMR element having the tunnel barrier layer and cannot be applied to a GMR element.
However, in order to realize a current sensor which uses a GMR element that can measure current from a relatively low current to a high current with high accuracy, it is necessary to widen an output linearity range which is a range in which the output has linearity with respect to a change in the magnetic field of the GMR element while suppressing the hysteresis of the GMR element. There are two methods to widen the output linearity range. The first method is to increase shape magnetic anisotropy by reducing the dimension of a long pattern of the GMR element in the width direction perpendicular to the longitudinal direction. However, there is a limit to a reduction in the dimension of the long pattern in the width direction, and the dimension in the width direction has been reduced to almost the limit due to the requirements such as a reduction in size and a reduction in cost. The second method is to increase the magnetic moment Ms·t of the free magnetic layer. However, in a method of increasing the magnetic moment Ms·t by increasing the film thickness t of the free magnetic layer in which a CoFe alloy and a NiFe alloy are laminated in the related art, the resistance change ratio ΔR/Rmin is significantly reduced.